security-misc/debian/control

## Copyright (C) 2012 - 2020 ENCRYPTED SUPPORT LP <adrelanos@riseup.net>
## See the file COPYING for copying conditions.

Source: security-misc
Section: misc
Priority: optional
Maintainer: Patrick Schleizer <adrelanos@riseup.net>
Build-Depends: debhelper (>= 12), config-package-dev, dh-apparmor
Homepage: https://github.com/Whonix/security-misc
Vcs-Browser: https://github.com/Whonix/security-misc
Vcs-Git: https://github.com/Whonix/security-misc.git
Standards-Version: 4.3.0

Package: security-misc
Architecture: all
Depends: python3, libglib2.0-bin, libpam-runtime, sudo, adduser, libcap2-bin,
 apparmor-profile-dist, helper-scripts, ${misc:Depends}
Replaces: tcp-timestamps-disable, anon-gpg-tweaks, swappiness-lowest
Description: enhances misc security settings
 Inspired by Kernel Self Protection Project (KSPP)
 .
  * Implements most if not all recommended Linux kernel settings (sysctl) and
 kernel parameters by KSPP.
 .
  * https://kernsec.org/wiki/index.php/Kernel_Self_Protection_Project
 .
 kernel hardening:
 .
  * deactivates Netfilter's connection tracking helper
 Netfilter's connection tracking helper module increases kernel attack
 surface by enabling superfluous functionality such as IRC parsing in
 the kernel. (!) Hence, this package disables this feature by shipping the
 `/etc/modprobe.d/30_security-misc.conf` configuration file.
 .
  * Kernel symbols in various files in `/proc` are hidden as they can be
 very useful for kernel exploits.
 .
  * Kexec is disabled as it can be used to load a malicious kernel.
 `/etc/modprobe.d/30_security-misc.conf`
 .
  * ASLR effectiveness for mmap is increased.
 .
  * The TCP/IP stack is hardened by disabling ICMP redirect acceptance,
 ICMP redirect sending and source routing to prevent man-in-the-middle attacks,
 ignoring all ICMP requests, enabling TCP syncookies to prevent SYN flood
 attacks, enabling RFC1337 to protect against time-wait assassination
 attacks and enabling reverse path filtering to prevent IP spoofing and
 mitigate vulnerabilities such as CVE-2019-14899.
 .
  * Avoids unintentional writes to attacker-controlled files.
 .
  * Prevents symlink/hardlink TOCTOU races.
 .
  * SACK can be disabled as it is commonly exploited and is rarely used by
 uncommenting settings in file `/etc/sysctl.d/30_security-misc.conf`.
 .
  * Slab merging is disabled as sometimes a slab can be used in a vulnerable
 way which an attacker can exploit.
 .
  * Sanity checks and redzoning are enabled.
 .
  * Memory zeroing at allocation and free time is enabled.
 .
  * The machine check tolerance level is decreased which makes the kernel panic
 on uncorrectable errors in ECC memory that could be exploited.
 .
  * Kernel Page Table Isolation is enabled to mitigate Meltdown and increase
 KASLR effectiveness.
 .
  * Enables all mitigations for CPU vulnerabilities and disables SMT.
 .
  * A systemd service clears System.map on boot as these contain kernel symbols
 that could be useful to an attacker.
 `/etc/kernel/postinst.d/30_remove-system-map`
 `/lib/systemd/system/remove-system-map.service`
 `/usr/lib/security-misc/remove-system.map`
 .
  * Coredumps are disabled as they may contain important information such as
 encryption keys or passwords.
 `/etc/security/limits.d/30_security-misc.conf`
 `/etc/sysctl.d/30_security-misc.conf`
 `/lib/systemd/coredump.conf.d/30_security-misc.conf`
 .
  * The thunderbolt and firewire kernel modules are blacklisted as they can be
 used for DMA (Direct Memory Access) attacks.
 .
  * IOMMU is enabled with a boot parameter to prevent DMA attacks.
 .
  * Bluetooth is blacklisted to reduce attack surface. Bluetooth also has
 a history of security concerns.
 https://en.wikipedia.org/wiki/Bluetooth#History_of_security_concerns
 `/etc/modprobe.d/30_security-misc.conf`
 .
  * A systemd service restricts `/proc/cpuinfo`, `/proc/bus`, `/proc/scsi` and
 `/sys` to the root user only. This hides a lot of hardware identifiers from
 unprivileged users and increases security as `/sys` exposes a lot of
 information that shouldn't be accessible to unprivileged users. As this will
 break many things, it is disabled by default and can optionally be enabled by
 running `systemctl enable hide-hardware-info.service` as root.
 `/usr/lib/security-misc/hide-hardware-info`
 `/lib/systemd/system/hide-hardware-info.service`
 `/lib/systemd/system/user@.service.d/sysfs.conf`
 `/etc/hide-hardware-info.d/30_default.conf`
 .
  * The MSR kernel module is blacklisted to prevent CPU MSRs from being
 abused to write to arbitrary memory.
 .
  * Vsyscalls are disabled as they are obsolete, are at fixed addresses and are
 a target for ROP.
 .
  * Page allocator freelist randomization is enabled.
 .
  * The vivid kernel module is blacklisted as it's only required for testing
 and has been the cause of multiple vulnerabilities.
 .
  * An initramfs hook sets the sysctl values in `/etc/sysctl.conf` and
 `/etc/sysctl.d` before init is executed so sysctl hardening is enabled
 as early as possible.
 .
  * The kernel panics on oopses to prevent it from continuing to run a flawed
 process and to deter brute forcing.
 .
  * Restricts the SysRq key so it can only be used for shutdowns and the
  Secure Attention Key.
 .
  * Restricts loading line disciplines to `CAP_SYS_MODULE`.
 .
  * Restricts the `userfaultfd()` syscall to root.
 .
 Improve Entropy Collection
 .
  * Load `jitterentropy_rng` kernel module.
  `/usr/lib/modules-load.d/30_security-misc.conf`
 .
  * Distrusts the CPU for initial entropy at boot as it is not possible to
  audit, may contain weaknesses or a backdoor.
    * https://en.wikipedia.org/wiki/RDRAND#Reception
    * https://twitter.com/pid_eins/status/1149649806056280069
    * For more references, see:
    * `/etc/default/grub.d/40_distrust_cpu.cfg`
 .
  * Gathers more entropy during boot if using the linux-hardened kernel patch.
 .
 Uncommon network protocols are blacklisted:
 These are rarely used and may have unknown vulnerabilities.
 `/etc/modprobe.d/30_security-misc.conf`
 The network protocols that are blacklisted are:
 .
  * DCCP - Datagram Congestion Control Protocol
  * SCTP - Stream Control Transmission Protocol
  * RDS - Reliable Datagram Sockets
  * TIPC - Transparent Inter-process Communication
  * HDLC - High-Level Data Link Control
  * AX25 - Amateur X.25
  * NetRom
  * X25
  * ROSE
  * DECnet
  * Econet
  * af_802154 - IEEE 802.15.4
  * IPX - Internetwork Packet Exchange
  * AppleTalk
  * PSNAP - Subnetwork Access Protocol
  * p8023 - Novell raw IEEE 802.3
  * p8022 - IEEE 802.2
 .
 user restrictions:
 .
  * remount `/home`, `/tmp`, `/dev/shm` and `/run` with `nosuid,nodev`
 (default) and `noexec` (opt-in). To disable this, run
 `sudo touch /etc/remount-disable`. To opt-in `noexec`, run
 `sudo touch /etc/noexec` and reboot (easiest).
 Alternatively file `/usr/local/etc/remount-disable` or file
 `/usr/local/etc/noexec` could be used.
 `/lib/systemd/system/remount-secure.service`
 `/usr/lib/security-misc/remount-secure`
 .
  * A systemd service mounts `/proc` with `hidepid=2` at boot to prevent users
 from seeing each other's processes.
 .
  * The kernel logs are restricted to root only.
 .
  * The BPF JIT compiler is restricted to the root user and is hardened.
 .
  * The ptrace system call is restricted to the root user only.
 .
 restricts access to the root account:
 .
  * `su` is restricted to only users within the group `sudo` which prevents
 users from using `su` to gain root access or to switch user accounts.
 `/usr/share/pam-configs/wheel-security-misc`
 (Which results in a change in file `/etc/pam.d/common-auth`.)
 .
 * Add user `root` to group `sudo`. This is required to make above work so
 login as a user in a virtual console is still possible.
 `debian/security-misc.postinst`
 .
  * Abort login for users with locked passwords.
 `/usr/lib/security-misc/pam-abort-on-locked-password`
 .
  * Logging into the root account from a virtual, serial, whatnot console is
 prevented by shipping an existing and empty `/etc/securetty`.
 (Deletion of `/etc/securetty` has a different effect.)
 `/etc/securetty.security-misc`
 .
  * Console Lockdown.
 Allow members of group 'console' to use console.
 Everyone else except members of group
 'console-unrestricted' are restricted from using console using ancient,
 unpopular login methods such as using `/bin/login` over networks, which might
 be exploitable. (CVE-2001-0797) Using pam_access.
 Not enabled by default in this package since this package does not know which
 users shall be added to group 'console' and would break console.
 `/usr/share/pam-configs/console-lockdown-security-misc`
 `/etc/security/access-security-misc.conf`
 .
 Protect Linux user accounts against brute force attacks.
 Lock user accounts after 50 failed login attempts using `pam_tally2`.
 `/usr/share/pam-configs/tally2-security-misc`
 .
 informational output during Linux PAM:
 .
  * Show failed and remaining password attempts.
  * Document unlock procedure if Linux user account got locked.
  * Point out, that there is no password feedback for `su`.
  * Explain locked (root) account if locked.
  * `/usr/share/pam-configs/tally2-security-misc`
  * `/usr/lib/security-misc/pam_tally2-info`
  * `/usr/lib/security-misc/pam-abort-on-locked-password`
 .
 access rights restrictions:
 .
  * Strong Linux User Account Separation.
 Removes read, write and execute access for others for all users who have
 home folders under folder `/home` by running for example
 "chmod o-rwx /home/user"
 during package installation, upgrade or pam `mkhomedir`. This will be done
 only once per folder in folder `/home` so users who wish to relax file
 permissions are free to
 do so. This is to protect previously created files in user home folder which
 were previously created with lax file permissions prior installation of this
 package.
 `debian/security-misc.postinst`
 `/usr/lib/security-misc/permission-lockdown`
 `/usr/share/pam-configs/mkhomedir-security-misc`
 .
  * SUID / GUID removal and permission hardening.
 A systemd service removed SUID / GUID from non-essential binaries as these are
 often used in privilege escalation attacks.
 It is disabled by default for now during testing and can optionally be enabled
 by running `systemctl enable permission-hardening.service` as root.
 https://forums.whonix.org/t/disable-suid-binaries/7706
 `/usr/lib/security-misc/permission-hardening`
 `/lib/systemd/system/permission-hardening.service`
 `/etc/permission-hardening.d/30_default.conf`
 .
 access rights relaxations:
 .
 Redirect calls for `pkexec` to `lxqt-sudo` because `pkexec` is incompatible
 with `hidepid`.
 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=860040
 https://forums.whonix.org/t/cannot-use-pkexec/8129
 `/usr/bin/pkexec.security-misc`
 .
 This package does (not yet) automatically lock the root account password.
 It is not clear that would be sane in such a package.
 It is recommended to lock and expire the root account.
 In new Whonix builds, root account will be locked by package
 dist-base-files.
 https://www.whonix.org/wiki/Root
 https://www.whonix.org/wiki/Dev/Permissions
 https://forums.whonix.org/t/restrict-root-access/7658
 However, a locked root password will break rescue and emergency shell.
 Therefore this package enables passwordless rescue and emergency shell.
 This is the same solution that Debian will likely adapt for Debian
 installer.
 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=802211
 Adverse security effects can be prevented by setting up BIOS password
 protection, grub password protection and/or full disk encryption.
 `/etc/systemd/system/emergency.service.d/override.conf`
 `/etc/systemd/system/rescue.service.d/override.conf`
 .
 Let the kernel only swap if it is absolutely necessary.
 `/etc/sysctl.d/30_security-misc.conf`
 .
 Disables TCP Time Stamps:
 .
 TCP time stamps (RFC 1323) allow for tracking clock
 information with millisecond resolution. This may or may not allow an
 attacker to learn information about the system clock at such
 a resolution, depending on various issues such as network lag.
 This information is available to anyone who monitors the network
 somewhere between the attacked system and the destination server.
 It may allow an attacker to find out how long a given
 system has been running, and to distinguish several
 systems running behind NAT and using the same IP address. It might
 also allow one to look for clocks that match an expected value to find the
 public IP used by a user.
 .
 Hence, this package disables this feature by shipping the
 `/etc/sysctl.d/30_security-misc.conf` configuration file.
 .
 Note that TCP time stamps normally have some usefulness. They are
 needed for:
 .
  * the TCP protection against wrapped sequence numbers; however, to
   trigger a wrap, one needs to send roughly 2^32 packets in one
   minute:  as said in RFC 1700, "The current recommended default
   time to live (TTL) for the Internet Protocol (IP) [45,105] is 64".
   So, this probably won't be a practical problem in the context
   of Anonymity Distributions.
  * "Round-Trip Time Measurement", which is only useful when the user
   manages to saturate their connection. When using Anonymity Distributions,
   probably the limiting factor for transmission speed is rarely the capacity
   of the user connection.
 .
 Application specific hardening:
 .
  * Enables APT seccomp-BPF sandboxing. `/etc/apt/apt.conf.d/40sandbox`
  * Deactivates previews in Dolphin.
  * Deactivates previews in Nautilus.
  `/usr/share/glib-2.0/schemas/30_security-misc.gschema.override`
  * Deactivates thumbnails in Thunar.
  * Enables punycode (`network.IDN_show_punycode`) by default in Thunderbird
   to make phishing attacks more difficult. Fixing URL not showing real Domain
   Name (Homograph attack).
  * Security and privacy enhancements for gnupg's config file
   `/etc/skel/.gnupg/gpg.conf`. See also:
   https://raw.github.com/ioerror/torbirdy/master/gpg.conf
   https://github.com/ioerror/torbirdy/pull/11
 .
 Want more? Look into these:
 .
  * Linux Kernel Runtime Guard (LKRG)
  * tirdad - TCP ISN CPU Information Leak Protection.
  * Whonix ™ - Anonymous Operating System
  * Kicksecure ™ - A Security-hardened, Non-anonymous Linux Distribution
  * SecBrowser ™ - A Security-hardened, Non-anonymous Browser
  * And more.
  * https://www.whonix.org/wiki/Linux_Kernel_Runtime_Guard_LKRG
  * https://github.com/Whonix/tirdad
  * https://www.whonix.org
  * https://www.whonix.org/wiki/Kicksecure
  * https://www.whonix.org/wiki/SecBrowser
  * https://github.com/Whonix
 .
 Discussion:
 .
 Happening primarily in Whonix forums.
 https://forums.whonix.org/t/kernel-hardening/7296